Gear honing tool



- Nov. 24, 1959 w. s. PRAEG ET AL GEAR HONING TOOL Fi-led'S ept. 4. 1957 INVENTORS WALTER S.PRAEG JOHN \Lslwzg ATTORNEYS United States Patent GEAR HONING TOOL Application September 4, 1957, Serial No. 681,971 8 Claims. (Cl. 51-206) The present invention relates to a gear honing tool, and is a continuation-in-part of our prior copending application Serial No. 543,704, filed October 31, 1955. I

It is an object of the present inventionto provide a gea-r honing tool in the form of a gear having teeth the surface portions of which to a substantial depth'are composed of a suitable relatively hard, strong, slightly yieldab'le and highly resistant resin compound having distributed therein a multiplicity of abrasive particles. 7

It is a further object of the present invention to provide a gear honing tool as described in the preceding paragraph in which the resin component of the compound is essentially epoxy resin.

It is a further object of the present invention to'provide a gear finishing hone as described in either of the preceding paragraphs in which the resin compound includes fiber particles as a reinforcing filler.

It is a further object of the present invention to provide a gear honing tool as described in any of the foregoing paragraphs in which the resin compound includes extreme- 'ly fine grit "for the purpose of rendering the compound wear resistant. I

2,913,858 Paten ed Nov. 24, 1959 therein and exposed at the surface thereof in position to be drawn in abrading or cutting relation across the surfaces of the teeth of the worl; gear as'the tool and work gear are rotated in mesh. In general, this has been accomplished by forming the tooth portions of the tool of an essentially hard, strong, slightly yieldable and highly resilient resin compound.

In general, the honing operation may be accomplished in two Ways. In some cases the hone and gear being finished are in relatively loose mesh, preferably at crossed axes, and the hone or gear is positively driven, thereby driving the other member of the pair in mesh, and rotation of the driven member may be opposed by a suitable 'braking action. Experience has indicated however, that'hest results are normally tobe anticipated when the hone and gear are rolled together in mesh at crossed axes under controlled relatively 'light radial pressure.

Referring now to the drawings there is illustrated a portion of a gear honing tool indicated generally at 10. The inner annularport-ion or core 12 may be formed of any suitable material such as metal but for convenience and economy, it is preferred to employ a resin compound which may be similar to the resin employed in the toothed portion of the hone except that it does not contain the abrasive grains or particles. The outer toothed portion indicated at 14, is formed of the-resin compound and has its teeth accurately shaped to be conjugate to the desired final form of the work gear to be finished. As indicated in Figure 2, this outer -tooth portion 14 of the bone contains a multiplicityof abrasive particles which are indicated therein.

More specifically, itis anobject of'the present invention to provide a gear finishing hone at least the tooth portions of which are formed of a resin compound {having an operating hardness in the range from 90 points above zero to 40 points below zero on the RockWell'M scale.

Other objects and featuresof the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying .drawing, illustrating a preferred embodiment .of the invention, wherein: 1

Figure 1 is a fragmentary elevational view :ofagear hone constructed in accordance with the present .invention.

Figure 2 is a-section on thelinef2+2,'Figure 1. In .the manufacture of gears highly accurate methods are availablefor finishing the profiles of gear teethtprior to hardening. However, after the gears have beenheat treated to harden the working surfaces of -the.:teeth,=the

only methods heretofore available forzfinishing the hardened surfaces of the teeth have been grinding and lapping.

Grinding is a slow and tedious process. :It also=haslthe t objection that in many cases'it tendsito burn the surfaces of the teeth and to produce stress areas where fatigue failure develops. i

Lapping is subject to the objections rthat it -;is aasslow and messy operation, involving the-use of lappingzfluid. Furthermore, lapping, which has heretofore'been carried out primarily with ,castiron laps, results iriamearing away of the lap comparable to the removal, ofv-material from the'hardened gear. tThus, "lap :life is :shortand tool cost is relatively expensive.

They present inventionrrelates to .a honingioperation "quite distinchbcthifrom grinding: andlapping. In accordance with therpresentiinventionithe toolisrin theiform .ot a ,gear at. least the-tooth portions of which. i are relatively shardsandstrcngsandcontain;abrasive particleslembedded hones wouldlbe prohibitive.

Inasmuch as the operating portion of the home, namely, the toothed portion 14 thereof, has a relatively large quantity of the extremely hard abrasive grains or particles therein, itwould be possible to finish the teeth of the home .to desired shape only by an expensive grinding or trimming process. If this were done the cost of the In accordance with the present invention the homes-are cast to final form and are ready for -use immediately upon .removal from the mold. Inasmuch as-the-Jhonqkto'be commercially acceptable, :must be produced by 'a final casting process, it is essential to form thehone f rom a-material having aflvery minimum shrinkage orrlinotherwords, to have a very highdegree of -dirnensional stability. S0 far as applicants :are aware, the only resin suitable-for commercial production of homes at the presenttime -is epoxy resin.

Inasmuch as mew-resins are constantly being developed,

and sincethe utility of the particular resin in the particular case is independent ofits chemical make-up, it-is of courseentirely" possible that in the future new resins diifering chemically :from epoxy resin but having the required physical properties now found onlyinf'epo xiy resin, may become available.

Epoxy resin isparticularly-suitable because of the ease :with which it may be cast. The epoxyresin is a thermal setting .resin which when-mixed with a hardener or catalystmayjbe cured atmoderate temperatures and will completely".cure:iri =a relatively short-time. A particular resinwhich: has proved the-most satisfactory in extended use is identifiedby the supplier, Marblette Corporation, as formula 1270A, in which the resincomponent is epoxy resinsupplied by the: Bakelite Corporation. To this is addedil ionite or1Carborundumg325 grit, and chopped glass fiber 1%, inch tin length. The compound may iu some I cases :contain .;some rubberizer which will increase :flexibility -awithout l'su-bstantially decreasing-hardness or tensile strength; The 'rubberizer added is identified by :the;supplie r, Marblette; Corporation, asNo. 2 rubberiz r iand mayzbe used-dn an amount not to exceed-;2'5%.

The Marblette- Corporation, supplier of the epoxy resin referred to above deseribes the epoxy resin as follows:

An epoxy resin suitable for this invention may be produced by reacting epichlorohydrin and bisphenol A in the presence of a sodium hydroxide solution in water. The reaction is carried out at a temperature of about 100 degrees centigrade. After the condensation reaction has taken place, the resin is freed of residual epichlorohydrin and is washed Well to remove salt and soluble by-products. The reaction is carried out to produce a reaction product having an average molecular weight of approximately 400. The resin is a liquid. The epoxy value, equiv./100 gm. is 0.50. The hydroxyl groups per molecule are 0.14-0.28.

A suitable curing agent is an aliphatic polyamine such for example as diethylene triamine. This compound when mixed as described herein may be satisfactorily cured in four hours between 125 and 150 degrees Fahrenheit.

The fine abrasive particles incorporated in the resin compound by the supplier are for the purpose of rendering the resin wear resistant' and are not for the purpose of producing an essentially abrasive article. The latter function is supplied by the addition of relatively large grit abrasive with particle sizes ranging from 46 grit to 100 grit silicon carbide. These particles are mixed uniformly in the resin compound and are cast into the annular tooth form in a suitable accurately formed mold.

Satisfactory results have been obtained when the abrasive particles are mixed uniformly through the resin compound just prior to casting. 1

There has been found to be a definite relationship between strength and shock resistance of the material of the homes with the size of grit employed. Excellent results have been obtained employing 60 grit silicon carbide. However, on very fine pitch teeth improved strength characteristics are observed if a finer grain abrasive, as for example 100 grit, is employed. a

A second factor controlling the selection of the grit size is of course the type of surface finish desired. In one hone which was designed particularly to produce a three to five micro inch surface finish on gear teeth, the abrasive particles in the hone were 280 grit. It would appear that so far as surface finish is concerned it would never be necessary to use smaller than 280 grit. However, for extremely fine pitch gears as for example 92 pitch, the dimensions of the teeth on the hone are so small that it may be desirable to use abrasive'grains having a grit size as small as 500 grit.

Conversely, on very coarse pitch gears, and particularly where surface finish is not critical, grit size as large as 46 or even larger is practical.

Production of the gear hone by the following described method has proven satisfactory: In the first place, a metal gear is accurately finished to the exact dimensions and specifications required in the hone. The tooth surfaces of this metal gear are treated with a suitable parting compound such for example as wax. This gear is placed in a suitable container and resin compound in liquid phase is poured into the container to surround the gear. The resin compound is preferably the epoxy resin compound with the relatively large abrasive particles omitted therefrom. This material is characterized by high dimenstonal stability. The resin compound is then caused to set by the application of heat. When the material has set, the metal gear isremoved, the parting agent permitting ready separation.

The hollow moldthus produced reproduces the characteristics of the master metal gear with extremely high fidelity. To produce the hone, a core such as that illustrated at 12 in Figure 1, is accurately centered within the mold leaving an annular space for the reception of the resin compound containing the relatively large abrasive particles. This material in fluid phase and including the catalyst or hardener, is poured into the space. between the core and the mold, the inner surfaces of the mold havmg been treated with a suitable parting compound.

Again, the resin compound is caused to set by heating, excellent results having been obtained when heated at a temperature of approximately 180 degrees Fahrenheit. Best results have been obtained when the cure is continued for a hour and a half, the hone permitted to cool and then given a second cure of approximately an hour. This is found to produce better results than a single cure of two and one-half hours duration.

The Marblette epoxy casting resin which is supplied by the Marblette Corporation, has before the addition of the relatively coarser abrasive particles, a compressive strength in excess of 20,000 pounds per square inch, a density of 100 pounds per cubic foot, an impact resistance of 1.5 ft.-lbs./in. notch, a shrinkage of .0007 inch per inch, and a thermal expansion of 6.5 times 10 inches per inch. The hardness of the completed hone with the relative coarse abrasive particles included has been varied from on the Rockwell M scale to a reading of 40 points below zero on this scale, and within this substantial range of hardness commercially satisfactory results have been attained. 4

The essential physical properties which appear to explain the operating efiiciency of homes constructed in accordance with the present invention is the support of the individual abrasive particles in a very hard material which is nevertheless slightly yieldably and highly resili- .ent. Thus, the abrasive particles are firmly held in the surface of the hone and are dragged thereby across the surface of the teeth of the hardened gear being honed. As a result, the bone is found to be extremely free-cutting and exhibits a useful life many times greater than that attainable with cast iron laps.

A feature of the invention which of course is an essential requisite for the production of accurate gears is the ability of the teeth of the hone to hold the exactly predetermined form cast therein. At the same time, the material cannot be a brittle material such for example as commonly employed in grinding wheels, since it is inherent in the operation in mesh with the work gear that local distortion of surface portions of the teeth of the hone takes place. This is permitted because of the slight yieldability of the material. This may be characterized essentially as a lack of brittleness which prevents crumbling of the material of the bone under load. Accompanied with the property of slight yieldability is the property of high resilience so that instantaneously upon release of the load which has caused small surface portions of the teeth of the hone to yield, the material will move back to its initial position. This yieldability accompanied by instantaneous resilient retraction permits a heavily stressed abrasive particle to yield slightly when encountering a relatively high point in the surface of the work gear. As the abrasive particle is thus dragged across the high point, a relatively greater pressure is exerted between the abrasive particle and the surface of the work gear, with consequent increase in removal of material. Thus, not only does the relatively hard, slightly yieldable and highly resilient resin compound prevent crumbling of the hone and breaking out of abrasive particles under load, but it also automatically concentrates the abrading or finishing action on the high zones or areas of the teeth of the gear which require the most removal of metal.

The highly successful operation of this hone in commercial production is thus probably attributable to two factors. The first of these is that the proportion of resin to the abrasive particles is sufiicient to provide a solid or substantially solid matrix in which the individual particles are separately embedded. This is to be contrasted with a structure which would result from providing only sufiicient bonding agent to unite the abrasive grains in a porous or spongy construction. The second of these of course is the physical properties of the particular resin and these properties are divided into two groups. The first group of properties are those which render the material suitable for the production of sufl'iciently accurate characteristics ifg'ear honing' tools by "casting, and l further, '"from th'e comcurate tooth form 'while at the same time 'having a lack of brittleness which would render tool life unacceptably short. This lack of brittleness may be expressed as a certain limited 'yieldability accompanied *bylasti'c return "to 'theposition occupied before yielding. Thus, a

particular abrasive particle when too heavily s'tressed will yield very slightly and thus prevent it "from being torn outo'f its embeddedmatrix. This -yieldingaof course is accompanied by an increase in pressure existing between the abrasive grain and thework with a'corresponding increase in removal of metal. As'soon asthe particle :is Zfreed from its stressed 'conditi on it returns substantially instantly to its initial position where it 'againis available for producing an accurate machined-surface.

Ihis limited yieldability of the material which permits the embedded abrasive "particles *to yield when over stressed and to return totheir initial posit ion account-s for the unexpectedly long tool "life which permits 'asingle -h'on'e to finish under idea'l conditions 10,000 or more work pieces.

While reference is made to yieldability, it shouldibe understood that'this does not :implyin any sense that the tool is soft or rubbery. The actual hardness of the material as :measured on the Rockwell M-scale indicates a relatively hard material. The cast surfac'e of 1a lhone .produced in accordance "with the present invention aprpears :quite hard and when tapped by Ja hard object asoundsaand actsias' though itiwere perfectly hard. .Thus, the 1 tool apparently has the characteristic in operation of acting under Snormal condition's as thoughiit was perfect- -ly hard with no appreciable yieldability soithat removal .of metalfrom a hardened gear istperfectlytpractical'with- .out appreciable distortion 1 of tthe material of the I teeth of the hone. his only when exceptional severe localize'd stresses occur that .theyieldabilitycof ithe material comes .into 'playito'preventifracturepr1tearing out=..of anwover- "stressed abrasivelparti'cle.

It ;is because "these SPIOPEI'TIcS are presentiin ahones constructed in accordance with the present invention that the honesihaverproven themselvestobe extremely successful in commercialproduction whereas many prior attempts to produce commercially feasible gear honing toolshave met with uniform failure.

While the present -honeis useful in at {general'flinishing -operation =to improve-all -tooth"characteristics, has a particular utility-in the -removal -'of nicks and rriinor -imperfections 'nhardened work -gears. It will-be readily apparent that in its operation of removing nicks =and the "accompanying outstanding small projections, the working surfaces of theteeth ofthe hone are subjeeted to ex- 'ceptionall-y severelocalstresses. -If'the material ofthe hone were not definitely -yieldable under the extremely hi gh.unitpressures thus .appliedgit will be ia'ppreciated that passageiof-a nickbnatoothacross the surface (if a t'ooth of-the hone --would -seore the hon'e tooth or other wise injure it. Such however, is not the case and hones constructed in accordance with the present invention have successfully operated to remove nicks and local imperfections from any thousands of gears per hone.

The hone constructed in accordance with the present invention is operated in mesh, preferably at crossed axes,

earsese 6 with the work gear, whichtmay be. hardened previously to the-honing ioperation. While the hone :and gear may be driven: in n'iesh zia't zsubstantial :speeds, :such for exampleiasiaipitch line velocityof 1000 or more feetper minute, it will be appreciatedIthat -the relative sliding movement between the surfaces .of the teeth of the hone and gear is :much :slower 'and variable fromua .minimum at an operatingpitch line to a maximumadjacent the top and bottom portions of 'the teeth. -At.the;pitch line, with the gear and hone tat crossed axes, the relative sliding action which results .in honing of the teeth of the gear is due only to thecrossed axestrelationship and is a function ofthe angle inspace betweenbthe-axes of the gear and hone.

The honing tooliproducedin accordance-with the present inventionlisa substantially solid or dense structure. The proportionate quantity of resin abrasive grains is such tastto produce a solid-structure as contrasted with a porous'or spongy structure characteristicof certain grinding wheels, in which only 'sufficient bonding material is present to interconnect.adjacentgrains of abrasive. Particularly,when .a'finerssgrit size abrasiveis used,the material of the presenthones has all theappearance of 63.

perfectly h'omogeneoussolid material, appearing almost 1ikemetal on its .smooth cast surfaces. Even when the materialis5fractured, the exposed surfacepresents the impression ;of a perfectly uniform homogeneous solid dense material.

Perhapsthe feature which distinguishes thepresent material over.materialifrom which attemptshave'been made in-the past to producesh'oning or abradingtools is in the relatively high proportion of resinsso that each of the abrasive grains is'in effect surrounded and embedded .in

.resin,:ratherthan beingb'onded'at a: limited contact area with adjacent grains. While ithe proportionof grains is normally quite large, neverthelessthezproportion of resin inthe material1isisufiiciently great to zprevent the occurrence :of .any appreciable number of voidsinthe-solid material.

Emphasis 'has :been placed upon the fact that the hone disclosed hereinisacast in Efinal form. Gnlyby casting the toothed portion of tthe. hone to ?its :final operating form isit commercially practical:to produce-honing'tools.

This in turn is ".possible only when employing a resin compound having the requiredhigh degree of dimensional stability which permits accurate reproduction first of a mastergear'to produce'the mold,'and second, ofa hone to reproduce the form of the mold. The only resin which applicants have been abletto discover having the requisite dimensionalstability is epoxy .resin. Fortunately, this resin has physical properties when combined as disclosed herein, which are suitable for a hone and which permit longlifein honing'and finishing hardenedrgears. The physical properties, besides 'the normally expected strength characteristics, are the combination of substantial hardnessaccompanied by slight but definitegyieldability andby ahigh iresilience so that when portions of 1 the materialv :are caused to yield by excessive localized loads, they are restored upon release of the load to their accurately cast form.

The factors of hardness, yieldability andresilience determine the life of r the-hone, and the test of hardness to determineRockwell M'hardnessjs 1a valuableindication both of=hardness and :yieldability.which'may be considered ingeneral asdependentuupon'thersame physical property. The aetual measurement is of'deflection under localized j pressure.

A specific example'ofea material which has proved highly satisfactory in extended commercial usage is.given below where the parts are referred to by weight:

Resin compound Material: Parts by weight Epoxy resin 100 Abrasive filler325 grit-silicon carbide 25-100 Glass fibersinch 10- 30 This material is purchased from the Marblette Corporation under the identifying number of 1270A.

Just prior to pouring the compound to produce the hones, the resin compound is mixed with abrasive such for example as silicon carbide particles having a grit size of from 46 to 280. Excellent results are attained when 100 parts of the resin compound as described above, are thoroughly mixed with 100-150 parts of the silicon carbide abrasive. Within this range, the resin and grains form a dense, solid material characterized by substantially no voids therein, the grains being essentially separated and embedded in and surrounded by the resin matrix. At this time a catalyst or hardener is added to the mixture, preferably between 15 and 20 parts per 100 parts of the resin compound. This'hardener is a conventional hardener for use in conjunction with epoxy resin, as for example an aliphatic-amine or poly-amine.

The hones constructed in accordance with the present invention may be in the form of cylindrical gears; that is, either spur or helical, and they may be either internal or external. Thus for example, a hone in the form of an external gear may be used to finish the teeth of an external or an internal work gear. Conversely, a hone in the form of an internal gear may be used to finish the teeth of an external work gear. The invention is not of course limited to cylindrical gears, but has particular advantage in the finishing of generally tapered gears such for example as bevel or hypoid gears.

While reference has been made in the foregoing to the fact that the material of the hone is essentially a solid resin compound having the abrasive particles embedded therein, it is recognized that in mixing'the abrasive particles with the resin compound while the resin compound is in liquid phase. it is impossible to avoid the introduction of some bubbles into the mixture. The mixing operation is carried out with extreme care, preferably under a substantial vacuum, to minimize and so far as possible eliminate the presence of bubbles in the finished material. Accordingly, where the resin com- :pound is defined as solid, it will be understood that it encompasses a material which is essentially solid even though some air bubbles may be included.

The use of epoxy resin in the resin compound has the additional advantage that epoxy resin exhibits extremely high adhesive properties with respect to the abrasive grains. Thus, a grain which is partly exposed and partly surrounded by the resin compound, is supported not only by the mechanical action of the resin in surrounding it, but also by adhesion existing between the interfaces of the resin compound and abrasive grain.

The drawing and the foregoing specification constitute a description of the improved gear honing tool in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What we claim as our invention is:

1. A gear hone comprising a gear-like body having teeth conjugate to the required tooth form of a gear to be finished, the surface portions of said teeth at least to a substantial depth comprising a solid cured epoxy resin compound having separated abrasive particles of a grit size of 46-280 embedded therein and exposed at the surface thereof, said cured resin compound having a hardness as measured on the Rockwell M scale between 90 above and 40 points below zero, but being slightly yieldable under excessive local pressure to prevent crumbling, and highly resilient to return immediately to exact initial form when relieved of the excessive local pressure.

2. A gear hone comprising a gear-like body having teeth conjugate to the required tooth form of a gear to be finished, the surface portions of said teeth at least to a substantial depthcomprising a solid cured epoxy resin compound having separated abrasive particles of a grit size of 46-280 embedded therein and exposed at the surface thereof, said cured resin compound having a hardness as measured on the Rockwell M scale between points above and 40 points below zero, but being slightly yieldable under excessive local pressure to prevent crumbling, and highly resilient to return immediately to exact initial form when relieved of the excessive local pressure, said compound having a mold shrinkage not greater than .001 inch per inch.

3. A gear finishing hone of cast gear-like form having teeth at least the surface portions of which are an epoxy resin compound comprising approximately parts by weight of epoxy resin, 25-100 parts fine grit abrasive filler, to which compound is mixed 100-150 parts of abrasive particles of 46-280 grit size and 15-25 parts hardener per 100 parts of compound.

4. A gear finishing hone as defined in claim 3 in which the epoxy resin compound includes 10-30 parts by weight of short glass fibers per 100 parts by weight of the epoxy resin.

5. A gear hone comprising a gear-like body having an annular toothed portion provided with teeth conjugate to the required tooth form of a gear to be finished, at least the annular toothed portion of said hone being cast to final form and being formed of a solid epoxy resin compound having abrasive particles of grit size 46-280 embedded therein and exposed at the surface thereof, said annular toothed portion having a hardness of between 90 above and 40 below zero on theqRockwell M scale.

6. A hone as defined in claim 5 in which the annular toothed portion of the bone comprises 100-150 parts by weight of the abrasive particles per 100 parts of the resin compound.

7. A hone as defined in claim 6 in which the epoxy resin compound comprises 25-100 parts byweight of a fine grit abrasive filler per 100 parts of epoxy resin.

8. A gear hone comprising a gear-like body having an annular core, an annular toothed portion connected to said core and provided with teeth conjugate to the required tooth form of a gear to be finished, at least the annular toothed portion of saidhone being cast to final form and being formed of a solid epoxy resin compound having abrasive particles of grit size 46-280 embedded therein and exposed at the surface thereof, said annular toothed portion having a hardness of 'between 90 above and 40 below zero on the Rockwell M scale.

References Cited in the file of this patent UNITED STATES PATENTS 1,912,216 Page May 30, 1933 2,027,090 Carter Jan. 7, 1936 2,051,558 Voegeli-Jaggi Aug. 18, 1936 2,073,590 Sanford Mar. 9, 1937 2,097,803 Sanford Nov. 2, 1937 2,105,896 Stubbs Jan. 18, 1938 2,113,185 Thilenius et al. Apr. 5, 1938 2,165,386 Klomp July 11, 1939 2,189,733 Kistler Feb. 6, 1940 2,218,795 Kistler Oct. 22, 1940 2,351,842 Seibold June'20, 1944 2,521,911 Owen Sept. 12, 1950 2,779,668 Daniels et a1. Jan. 27, 1957 

